Ultraviolet radiation exposure of mammalian eyes has been associated with the growth of the eye disease pterygia and the promotion of the conversion of pinguecula to pterygia (American Academy of Opthalmology, Basic and Clinical Science Course, Cornea Section 4, Retina Vitress 1987-1988 Edition, pp. 72-73).
Pinguecula is a benign eye disease in which a yellow, triangular patch forms on the conjunctiva and covers the sclera. When such a patch encroaches onto the cornea and forms a thickened, vascular and wing-shaped area of the conjunctiva the resulting condition is known as pterygia which may block the visual axis. It is known that ultraviolet light irritates the outer membranes of the eye and further stimulates the conversion of one disease into another. A theoretical possibility of the role of UV light in the formation of tumors in the retina, such as melanoma, may exist. Also non entity called "solar retinopathy" has been described in which the retina may be damaged by UV light (Ham, W. T., et al., Solar Retinopathy as a Function of Wavelength: Its Significance for Protective Eyewear, pp. 319-346; Ham W. T., Ocular Hazards of Light Sources, Review of Current Knowledge. J. Occup. Med. 25: 101-103, 1983.
The only means known in the art to shield the outer eye membranes from harmful ultraviolet radiation having a wavelength in the range of 290-320 nanometers, is the physical blocking of the radiation by means of sunglasses or other sunscreen devices physically attached to the face or head of the user. There are no opthalmic sunscreen agents known in the prior art until now.
Various compositions and mixtures thereof were considered for use as the opthalmic agent in the inventive method and discarded as ineffective. For example, p-aminobenzoic acid (PABA) blocks UV radiation but is too irritating to the delicate tissues of the eye and interferes with other antibiotic solutions which may be used by the patient following surgical removal of the pterygia bodies. Additionally, preparation of a solution containing PABA for use in the eye is quite costly.
Existing opthalmic solutions which may be obtained commercially without a prescription and which are used to lubricate eye tissues forming artificial tears to relieve irritation of the eyes are known. In general, these known solutions may be divided into two types: eyedrop solutions containing polyvinylchlorides and those containing hydroxypropylmethylcellulose.
Polyvinylchloride containing solutions were found to be wholly ineffective in blocking UV radiation from the eyes as illustrated in Table 1 infra.
It has been unexpectedly shown that hydroxpropylmethylcellulose containing compositions do effectively block UV radiation and thus may help prevent the occurrence of solar related ocular pathology as discussed above.